The present invention relates to bone fixation systems and, more particularly, absorbable or nonabsorbable bone fixation pins of the type for fixing soft tissue or tendons to bone or for securing two or more adjacent bone fragments or bones together.
Bones which have been fractured, either by accident or severed by surgical procedure, must be kept together for lengthy periods of time in order to permit the recalcification and bonding of the severed parts. Accordingly, adjoining parts of a severed or fractured bone are typically clamped together or attached to one another by means of a pin or a screw driven through the rejoined parts. Movement of the pertinent part of the body may then be kept at a minimum, such as by application of a cast, brace, splint, or other conventional technique, in order to promote healing and avoid mechanical stresses that may cause the bone parts to separate during bodily activity.
The surgical procedure of attaching two or more parts of a bone with a pin-like device requires an incision into the tissue surrounding the bone and the drilling of a hole through the bone parts to be joined. Due to the significant variation in bone size, configuration, and load requirements, a wide variety of bone fixation devices have been developed in the prior art. In general, the current standard of care relies upon a variety of metal wires, screws, and clamps to stabilize the bone fragments during the healing process. Following a sufficient bone healing period of time, the percutaneous access site or other site may require re-opening to permit removal of the bone fixation device.
Long bone fractures are among the most common encountered in the human skeleton. Many of these fractures and those of small bones and small bone fragments must be treated by internal and external fixation methods in order to achieve good anatomical position, early mobilization, and early and complete rehabilitation of the injured patient.
The internal fixation techniques commonly followed today frequently rely upon the use of Kirschner wires (K-wires), intramedullary pins, wiring, plates, screws, and combinations of the foregoing. The particular device or combination of devices is selected to achieve the best anatomic and functional condition of the traumatized bone with the simplest operative procedure and with a minimal use of foreign-implanted stabilizing material. A variety of alternate bone fixation devices are also known in the art, such as, for example, those disclosed in U.S. Pat. No. 4,688,561 to Reese, U.S. Pat. No. 4,790,304 to Rosenberg, and U.S. Pat. No. 5,370,646 to Reese, et al.
Notwithstanding the common use of the K-wire to achieve shear-force stabilization of bone fractures, K-wire fixation is attended by certain known risks. For example, a second surgical procedure is required to remove the device after healing is complete. Removal is recommended, because otherwise the bone adjacent to an implant becomes vulnerable to stress shielding as a result of the differences in the modulus of elasticity and density between metal and the bone.
In addition, an implanted K-wire may provide a site for a variety of complications ranging from pin-tract infections to abscesses, resistant osteomyelitis, septic arthritis, and infected nonunion.
Another potential complication involving the use of K-wires is in vivo migration. Axial migration of K-wires has been reported to range from 0 mm to 20 mm, which can both increase the difficulty of pin removal as well as inflict trauma to adjacent tissue.
As conventionally utilized for bone injuries of the hand and foot, K-wires project through the skin. In addition to the undesirable appearance, percutaneously extending K-wires can be disrupted or cause damage to adjacent structures such as tendons if the K-wire comes into contact with external objects.
Notwithstanding the variety of bone fasteners that have been developed in the prior art, there remains a need for a bone fastener of the type that can accomplish shear-force stabilization with minimal trauma to the surrounding tissue both during installation and following bone healing.
In addition, there remains a need for a simple, adjustable bone fixation device which may be utilized to secure soft tissue or tendon to bone.
There is provided in accordance with one aspect of the present invention, a fixation device for securing a first bone fragment to a second bone fragment. The fixation device comprises an elongate pin, having a proximal end and a distal end. At least one radially advanceable anchor is carried by the pin. An actuator, which is axially moveable with respect to the pin is also provided. The device includes at least one retention structure in between the pin and the actuator, for permitting proximal movement of the pin with respect to the actuator but resisting distal movement of the pin with respect to the actuator. Axial proximal movement of the pin with respect to the actuator causes at least a portion of the anchor to advance along a path which is inclined radially outwardly from the pin in the proximal direction.
The actuator may comprise a tubular body axially slidably carried on the pin. The anchor comprises at least one axially extending strip, having a free proximal end and a distal end, carried by the pin. The strip is moveable from an axial orientation to an inclined orientation in response to axial proximal retraction of the pin. In certain embodiments, at least two or four or more axially extending strips are provided.
The device may also comprise a hub carried by the pin. The distal end of the strip is connected to the hub. The hub preferably comprises an annular ring, axially movably carried by the pin. The hub may be fixed with respect to the pin.
The device may also include a first retention structure on the actuator for cooperating with a second retention structure on the pin to retain the device under compression. At least one of the actuator and the pin may comprise a bioabsorbable material, such as poly (L-lactide-co-D, L-lactide).
The distal end of the actuator may have a tapered surface, so that proximal retraction of the pin with respect to the actuator causes the anchor to incline outwardly as it slides along the tapered surface. The proximal end of the anchor may have a complementary tapered surface to slide along the tapered surface on the actuator. The pin may also have a relatively larger diameter near the distal end and a relatively smaller diameter proximally of the distal end.
In accordance with another aspect of the present invention, there is provided a bone fixation device for fixing two or more bone fragments. The fixation device comprises an elongate tubular body, having a proximal end, a distal end and a longitudinal axis. A distal anchor is on the fixation device, moveable from a low profile orientation for distal insertion through a bore in the bone to an inclined orientation to resist axial proximal movement through the bore. An elongate pin is axially moveable within the tubular body and associated with the anchor, such that proximal retraction of the pin with respect to the tubular body advances the distal anchor from the axial orientation to the inclined orientation.
The bone fixation device may also comprise at least one retention structure for retaining the anchor in the inclined orientation. The retention structure may comprise at least one ramped surface that inclines radially inwardly in the proximal direction. Alternatively, the retention structure includes at least one annular ridge. A first retention structure may be on the tubular body, and a second, complimentary retention structure may be provided on the pin.
The device may also comprise a proximal anchor. The distal anchor comprises at least two axially extending strips spaced circumferentially apart around the tubular body.
The tubular body may comprise a first tapered surface and the pin may comprise a second tapered surface such that proximal retraction of the pin with respect to the tubular body causes a radial enlargement of at least a portion of the tubular body.